The invention relates generally to a socket for testing an integrated circuit package. More particularly, the invention relates to a socket utilizing an improved contact pin structure which is able to reduce the electrical connection length between a to-be tested subject and a PCB to improve the high-frequency characteristic and has capability to maintain good electrical contact and extend the life of the socket.
Generally, an integrated circuit (IC) package is subjected to a test of its electrical characteristic using an open-top type socket for a handler or a manual socket of a Calm type. For this test, the socket is mounted on a printed circuit board (PCB) connected to measurement equipments. The IC circuit package is mounted on the socket. At this time, an electrical connection element, such as a contact pin is required for connecting the leads of the IC package to the terminals of the PCB.
In order to design a contact pin performing this function, the following four requirements should be considered. First, it should maintain good contact be with the tested subject. For this, the contact portion of the contact pin should maintain contact with the IC package while performing a wiping action. Second, it is required that the length of the electrical connection between contact points should be short as possible. In particular, when the contact pin is used to perform a high-frequency IC test, a long length of electrical connection may act as an impedance since the inductance of the contact pin becomes larger. Third, the contact pin should not cause any bending of an IC lead during the test. Bending of an IC lead during the test substantially degrades the yield of the IC. Fourth, the contact pin and the elastic members supporting them should have a long life. If any of the contact pins fails, the entire test socket should be replaced.
Various structures of contact pins in consideration of these requirements have been developed and used. FIGS. 1xcx9c3 are cross-sectional views of conventional contact pin structures mounted on a conventional socket according to their respective use.
The contact pin shown in FIG. 1 is so called Yamaichi socket pin, which is widely used in integrated circuit tester sockets. The Yamaichi socket pin, however, has the following disadvantages in view of the above four requirements. First, when a lead 12 of an IC 11 is pressed against the contact pin 10, some degree of wiping action is caused at a potion contacting a PCB terminal 13. As can be seen clearly from FIG. 1, the rotational radius of the contact portion of the terminal is short since a rotational axis of the contact pin 10 is very near to the PCB. Thus, it is difficult to perform wiping action in a wide area. Second, as the contact points of the integrated circuit lead 12 and the PCB terminal 13 are not aligned in a straight line and they are connected to each other via detouring path, there is a problem that the electrical length becomes longer. Third, when the pressure applied by the lead 12 of the integrated circuit 11, the floating suspension of the contact pin 10 is relatively small. Thus, when pressure is applied for test, the integrated circuit lead 12 may be bent since a great force is directly applied to the integrated circuit leas 12.
U.S. Pat. No. 4,445,735 was contrived to solve the problem of the Yamaichi socket pin. (see FIG. 2). However, this invention also has some limitations. First, it has a long electrical length. When pressure is applied, the integrated circuit lead can be bent since the floating suspension provided by the contact pin 20 when pressure is removed is limited. Thus, this invention achieves little improvement over the Yamaichi socket pin.
U.S. Pat. No. 5,069,629 illustrates improved electrical connection device over the Yamaichi socket pin or U.S. Pat. No. 4,445,735, the cross-sectional view of which is shown in FIG. 3. As can been seen from FIG. 3, the contact pin 30 of U.S. Pat. No. 5,069,629 has a structure in which contact points are aligned in a straight line to reduce the electrical length between the contact points. However, as the structure of the contact pin has a generally S-shape, it has a significant limitation in reducing the horizontal length of the contact portion. Thus, this structure is not able to minimize the electrical length. Also, as the displacement of the contact point on the side of the lead 32 of an integrated circuit 31 and that of the contact point on the PCB terminal 33 side are symmetric, if the contact point on the integrated circuit lead 31 has a downward displacement, displacement of the contact point on the side of the PCB terminal 33 should be upward. Also, axial axes of respective contact points are not same and have short rotation radius. Thus, although the contact pin structure provides some degree of wiping action, its wiping distance is very short.
It is therefore an object of the present invention to provide a socket for testing an integrated circuit using a contact pin structure which has a very short electrical length between the contact points, and does not cause bending of an integrated circuit lead during test, and which is able to maintain good contact state with the test subject and extend the life of the device.
In order to accomplish the above objects, the present invention proposes a socket for testing an integrated circuit including a plurality of contact pins for electrically connecting leads of an integrated circuit to terminals of a PCB spaced from the leads of the integrated circuit, being characterized by comprising a contact pin housing installed on said PCB for mounting said integrated circuit, said contact pin housing having a flat top surface and a flat bottom surface; a plurality of slots formed on both sides of the contact pin housing to pass through the contact pin housing from the top surface to the bottom surface and having a size adequate to accommodate the contact pins; a first channel and formed on both sides of the contact pin housing and a second channel formed in parallel to said first channel and on the outer side of the respective first channel, the channels being formed from the bottom surface of the contact pin housing and extending to cross all of the slots; a first elastic member and a second elastic member respectively installed within the first channel and the second channel, wherein the contact pins are inserted into the respective slots, and each of the contact pin engages with the first and second elastic members, and each of the contact pins includes a first contact portion protruding over the top surface of the contact pin housing for making contact with a lead of the integrated circuit and a second contact portion for making contact with one of the terminal of the PCB.
Also, the contact pin of the present invention is made of a thin and flat metal piece, said contact pin is characterized by including a first elastic member receiving portion having a circular circumferential face which is open toward and engage with the first elastic member when the contact pin is inserted into the slot; a second elastic member receiving portion having a circular circumferential face which is open toward and engage with the second elastic member when the contact pin is inserted into said slot, and said contact pin is further characterized in that the first elastic member receiving portion and the second elastic member receiving portion are formed on a upper side of the contact pin facing said first and second elastic members when the contact pin is inserted into the slot and the second elastic member is formed at a location opposing said first elastic member with respect to the center of the contact pin; and the first contact portion extends from the outer side of the first elastic member receiving portion with respect to the center of the contact pin and extends generally in a upward direction with respect to the upper side of the contact pin; and the second contact portion is formed on a bottom side of the upper side of the contact pin and at a location generally below the center of the contact pin.